A door such as a hollow core door typically includes two molded or flush door skins (sometimes called “door facings”) attached to opposite sides of an interior door frame, which is typically made of wood but sometimes metal or composites. The door facings are often molded from a composite of wood fiber and resin compound, although fiberglass-reinforced polymeric door facings and steel door facings are also known. The door frame typically includes stiles and rails positioned around the perimeter of the door that together form the frame. The interior of the door may optionally include a core.
Manual assembly of doors is relatively labor intensive, expensive, and subject to quality variations. During manual assembly, a door facing is placed on a production table with its intended exterior surface face down. Adhesive is applied, typically via a roll coater, to the opposite sides of the stiles and rails. The core and/or lock block(s), if any, are likewise coated. The adhesively coated frame parts (stiles and rails) are then placed by hand on the door facing on the table. Typically, the rails are placed at the top and bottom of the door facing, and the stiles are placed on opposite sides of the door facing. With the adhesive applied to a second upward-facing side of the stiles and rails, a second door facing is placed with its interior surface on the second side of the frame. Another door facing is then placed with its exterior surface face down on the previously assembled door and the process repeated until a stack of doors has been assembled. In this manual assembly process, the assembled doors should be handled carefully, given that the components of the door are in a loose “layup” state and can easily shift during transportation.
In the above-described manner, each successive door assembly is stacked on top of the previous door assembly until a predetermined quantity of door assemblies has been stacked. The stack of door assemblies is then transported to and loaded in a press. The press applies pressure to the entire stack for a period of time sufficient to allow the adhesive to bond the door facings to their respective frames. Conventional adhesives, such as polyvinyl acetate, may take approximately thirty minutes or more to cure or harden in the press before the door reaches “green” strength. The door achieves “green” strength when the adhesive has reached sufficient bonding strength to hold the door components together for further handling.
Once green strength is achieved, the doors may be removed from the press and moved to an in-process inventory until the adhesive reaches adequate cure strength. Depending upon the adhesive used and ambient conditions, the doors may need to remain in inventory for a relatively long period of time, for example two hours or more, or even as long as twenty-four hours, before the adhesive reaches adequate bonding strength for final processing.
After reaching adequate cure strength the doors are then moved to a final processing station. Final processing includes edge trimming the doors to customer specification and optional coating and/or painting of door skins and exposed edges of the stiles and rails around each door perimeter. Using this process, manufacturing time for a door may be twenty-four hours or more, from the time production is initiated to the resulting finished door is complete and ready for delivery to a customer or user.